d lnfreville



(No Model.) 5 Sheets-Sheet 1.

G. dINFREVILLE. Telephone Sy stem.

No. 234,578. Patented Nov.16, I880.

5. 8.1lba/a o 014/ ijw NPETERS, PHOTO-UTHOGRA (No Model.) 5 Sheets-Sheet 2.

G. dINPREVILLE; Telephone System.

Patented. Nov. 16, I880.

N. PETERS, PHOTO-LITHUGRAFNER, WASHINGTONv D C.

(No Model.)

BSheets-Sheet 3. G. dINFREVILLE. Telephone System.

Patented Nov. 16, 1.880.

5 Sheets-Sheet 4.

(No Model.)

e. dINFREVILLE. Telephone System. No. 234,578. Patented Nov. 16,1880.

5 Sheets-Sheet 5.

(No Model.) 7

' G. dINFR-EVILLE.

Telephone System.- v No. 234,578. Patented Nov. 16, I880.

iINrrnn S'ra'rns GEORGES DINFREVILLE, OF NEW YORK, N. Y., ASSIGNOR TO NATIONAL BELL TELEPHONE COMPANY.

TELEPHONE SYSTEM.

SPECIFICATION forming part of Letters Patent No. 234,578, dated November 16, 1880.

(No model.)

To all whom it may concern:

Be it known that I, GEORGES DINFREVILLE, of the city, county, and State of New York, have invented a new and useful Improvement in Telephone Systems, which invention is fully set forth in the following specification.

The object of my invention, broadly stated, is to accomplish with a single wire, emanating from a central office and passing through several outside stations, much or all of what is now accomplished with a separate wire from said central office to each of said stations.

By my invention, when used on a single wire connecting several stations with the central office, any station can call the central office and be automatically warned that its call has reached the said central office, and then communicate with the latter without interference from other stations. The central office can put itself in connection with any station at pleasure and call or communicate with that station to the exclusion of the others. The central office, while retaining at all times full control of the line, can call two stations successively, which can then be put in communication with each other, irrespective of their relative situation on the line, or it can at the same time put several stations in communication each with the one next to it on either side along the same line of wire, so that said stations can commu nicate with each other without interference. The invention is applicable to each of these purposes separately, and the whole or several parts can be combined with other known or suitable systems and forms of apparatus. It is also one of the objects of the invention to effect the above results with devices which are simple and uniform, or nearly so.

The invention is intended for telephonelines, district and fire-alarm telegraphs, buildings, and can be applied to burglar-alarms, rail- WaysignaIing, telegraph-lines, &c.

The nature and operation of my apparatus are as follows:

At the central office I provide a number of cells of battery so arranged that, either by reversal or by connecting different ends of the whole or of different sections of the battery to line, I can send a current of either polarity so desired. I provide at the central office and at each station a polarized relay, whose armature can move between two stops or contact-points having different electrical connections. For example, at each station outside of the central office one of said stops connects with the line leading to a more distant station, while the other connects with the ground and can make such station for the time being the terminus of the electric circuit. All these armatures are worked by polarized relays, and can therefore be thrown against one stop or the other, according to the polarity of the current sent over the wire from the source of electricity at the central office. Normally all these armatures are in contact with the line-stops; but by-depressing a key at either station or at the central office the main battery sends over the line a current of a certain polarity, which works an annunciator at the central office to call the at tention of the attendant and throws over to the other stops the armature of the polarized relay at the central office and at every station in the system. The movement thus caused in the armature at the central office establishes a new set of electrical connections with the linewire and throws upon it a current of different polarity. This current, passing through the line, closes it to the first station, there passes through the armature of its polarized relay,

throughits ground-stop, to earth but its spe- 8o cific polarity is such that it at once throws the armature of that station to its line-contact, and thus opens a path for the current and causes it to pass to the next station, where the same operation is repeated, and so on at each station successively, thus in turn making each station the terminal point of the line until the signalin g or desired station is reached. I then have a line from the central office grounded through the ground-wire at that station and cut off from 0 the ground-wire at each intermediate station. I place the signaling apparatus (telephone, telegraph-instrument, hell, or other alarm) of each station in its ground-wire, and I therefore arrive at a condition of things in which the cir- 5 I then have a circuit over which I can interchange conversation or other signals between the central office and the station calling. In like manner I can from the central office set into operation the batteries thereof, so that they shall first throw all the armatures of the outside stations to their ground-contacts, and then, by a current of opposite polarity operating on said polarized relays, as before stated, pick them up and replace them one by one on their line-contacts at each successive step, placing the stations one after another in circuit with the central ofiice. By suitable and convenient means at the central office the operator there attending can arrest this operation at any desired station, and thus place himself in direct circuit with that station, there sending the current to earth through the ground-wire, and therefore through the instrument placed in such groundwire. The circuit being thus established, he can, by any convenient signaling or other electrically worked apparatus, communicate with the station so selected.

My invention also consists in various forms or modifications of apparatus and combinations of apparatus or devices necessary or convenient for its operation, and which enable the operator at the central office to attain some results in addition to those thus indicated. Thus, for example, he can not only put the central otfice in communication with any outside station, but can put any station in direct communication with any other.

In order more fully to explain the invention and the manner of carrying the same into eifect, I proceed to describe a form of apparatus in which the same is embodied, reference being bad to the accompanying drawings, which form a part of this specification.

Similar letters of reference indicate corresponding parts. I

Figure 1 represents the part of the invention by which a station can call the central oflice. This part, when employed separately, is used mostly for district or fire-alarm telegraphs. The central olfice, O. Ofil, and two stat-ions, A and B, only are represented. The invention is not limited to any particular number of stations. Practice and the requirements of the service will determine how far their number may be safely extended but any more stations than represented would be connected and disposed like the two stations A and B.

Figs. 2 and 3, and Fig. 4. show different modifications of the electro-magnetie arrangement in the dial-indicator.

Fig. 5 shows an improved call-key to replace the key shown in Fig. 1 at the different stations.

Figs. 6 and 7 represent a suitable manner of constructing the district-boxes at the different stations.

Fig. 8 is a diagram showing an apparatus employed in connection with the dial-indicator for rendering constant the resistance of the portion of the line worked from the central ofiice and for dispensing with the resistances at the several stations.

Fig. 9 represents an arrangement whereby .one battery may be used in place of the two shown in Fig. 1.

Fig. 10 represents the part of my invention by which the person in charge at the central otfice can call. any station exclusive of the others, and also the disposition by which the intercommunication between the stations above referred to can be established. In Fig. 10 the system has been illustrated in connection with the use of telephones. It is not, however, limited to such use, as other well'known signalinginstruments could be used.

Fig. l 1 is an enlarged view of the key shown in Fig. 10, which is a cheaper and stronger form of the key illustrated in Fig. 5.

Fig. 12 shows the manner in which the Hughes cscapement may be made to take the place of the polarized relay at the central otfiee, and Fig. 13 an arrangement of springjacks whereby the same telephone at each station may be employed for communicating in either direction over the line.

In Fig. 14 a more convenient position for the condenser and also a modified arrangement of switch for connecting a larger battery gradually to line are represented.

In Fi 15 the manner in which the condenser at the central ofiice may be replaced by a small one at each station is shown.

In Figs. 16 and 17 are shown keys of another form for use at the stations, and in Figs. 18, 19, and 20 apparatus located at the central oflice, accomplishing, among others, the result for which the condenser represented in Figs. 10, 14, and 15 is employed.

Fig. 21 represents a relay which may be used at the central office and the stations in place of the relays shown in Fig. 1, and Figs. 22 and 23 forms of relays which may be used in the apparatus shown in Fig. 10 in place of the relays therein represented.

Referring particularly to Fig. 1, (3. Oil. is the central office, from which the line-wire L goes to the station A. It passes through the instruments of that station and emerges from it, as represented by L, to go similarly through the instruments at station B. If there are other stations, they are connected by a line, L, and so on according to the number of stations, and at the last station there is no further line connection 5 but the lefthand or line-contact point corresponding to m and m will have a ground connection through the key when closed, and the other, corresponding to n and a a direct and permanent groimd-connection, as shown in the full lines at stationsAand B, Fig. 1.

At the central office there is an apparatus for this line composed of four parts--viz., a po larized relay, R, an alarm, H g, a dial-indicator having a pointer, P, and operating magnet M, or instead of the indicator some other well-known signaling or recording instrument -as, for example, a Morse or chemical register or a printing-telegraphand one' or two main batteries. The connection between these several parts will be explained hereinafter. For every separate line-wire emerging from the central office there is a set containing or composed of the said four parts. \Vith the arrangement shown in Fig. lit may be possible, however, to work several lines from' the said batteries, which are represented by X and Y, and even to use the same indicator or register for several circuits, keeping, however, a distinctpolarized relay, R, and a distinct alarm, H g, for each circuit. The practicability of this operation will depend upon the number of calls likely to be made within a given time upon the different wires.

Station A includes a polarized relay, R, of the same dimensions as the polarized relay R, and a key, K. In its ground-wire an artificial resistance, 1", may be inserted for the purposes hereinafter explained.

Station 13 is arranged like station A, except that the resistance r in its ground-wire, if used, is less than 1", as will be also explained hereinafter.

The line-wire L from station B should remain open or be omitted if there are no more stations on the line. Otherwise the line runs through all the stations in the same manner, and they are all disposed like the two abovementioned stations A and B, except that the resistances in the ground-wires,if used, should successively decrease until the last one, which is oil. Each of these resistances should equal the resistance of all the line (instruments ineluded) between its station and the farthest station, including the relay at the last station. The linc-wire L on the line-wire emerging from the last station can, where practicable, return with advantage to the central office, 0. Off, for a reason explained hereinafter.

At central office, 0. Off., from the ground. plate Gr emerges the ground-wire, which is connected at 0 between the main batteries X and Y. same number of cells and are so arranged that were the ground-wire disconnected they would form a single battery with all its cells in tension-that is to say, the positive plate of the battery Y is connected at 0 to the negative plate of the battery X. The wire from the negative pole of the battery Y goes to the electro-magnet M of the dial-indicator, thence to the contact-point n in the polarized relay R. The wire from the positive pole of the battery X goes to the electro-magnet H, which is part of the alarm, the gong of the alarm being represented by g. I prefer to use here the wellknown electro-ma gnetic escapement of Hughes printing-telegraph, though some other wellknown form of alarm could be used. This escapement consists of a Hughes magnet with soft-iron armature, arranged to move by a strong spring when the magnetism ceases or diminishes, and by its movement release or move clock-work.

The two batteries have about the.

On leaving the electro-magnet H the wire runs to the bobbins of the polarized relay, R, which in the drawings is a Siemens polarized relay. In this relay the armature is preferably pivoted near to the pole-pieces, and its free end is prolonged by a spring, which with a large range of motion moves between the two contact stops at and n. Opposite the heavy part of the armature are two limiting-stops, p q, so adjusted that the spring end makes contact at mor n, and then, yielding to the pull of the electro-magnet, allows a still further motion to the armature before it is firmly arrested by the limiters p and q. The cores of the relay are made somewhat large in order to obtain a certain amount of magnetic inertia, and the spring may be made broad, like a fan, to make its motion sluggish. The pivot or hinge ofthe armature a is connected directly with the linewire L, which passes thence to station A, where it enters the coils of the polarized relay R, which latter is constructed like R, though with somewhat different electrical connections as appears in the drawings. On leaving the bobbins of It the wire is connected with the hinge of the armature a, which makes contact alternately at m and n, and is limited by stops 1) and q. The contact-stop a is connected permanently with the ground, as indicated at G, through theresistancer, if such be used. The stop m is connected with the key K, and can be temporarily connected with the ground G by the said key. It is also nected with the line-wire L, leading to station B, which is a repetition of A, except that the resistance 0' is less than a", as already stated, the parts corresponding to R, a, p, g, m, n, K, and G being indicated by R (9,19 1 m n K and G The operation of the system is as follows: When at rest the armatures a a a &c.,are all as represented in Fig. 1, being against the the left-hand contacts on m m and the polepieces and armatures of the relays R RR are all so adjusted that each armature will remain at whatever contact it happens to be when the current which has last moved it ceases to pass. \Vith the armatures in the condition indicated no currentpasses, because, although there is an unbroken connection from the battery X of 0. Off. through all the instruments of the different stations, there is no ground or return connection from either or any of them, and the circuit is thus normally open.

The Hughes electromagnetic escapement is adjusted in the well-known manner by means of the soft-iron armature, which can be moved along the permanent magnet placed at the back of the electro-magnet, and by adjusting the tension of the retractile spring at the back of the armature. The direction of the wire in the helices of electro-magnet H is such that the first current of even momentary duration which passes through it from battery X will destroy or sufficient-1y weaken the magnetism which holds the armature in prox.

imity to the cores, so that it abandons the armature to the action of the retractile spring, thus causing a single blow on the gong g. The clearness of the sound on the gong is insured by the proper adjustment of a back screw, which retains the solid part of the armature at such distance that the hammer placed at the end of the spring will rebound after striking the gong and keep clear of it.

The armature can be supplied with a tag or drop-plate, d, of any suitable material, placed at the end of a lever connected with or forming part of the armature, and a number or other mark can be inscribed upon such tag or drop-plate. This will be useful,it' several such alarms are placed in the same oflice, to indicate to the clerk in charge which bell has been ringing.

As in the Hughes apparatus, it is not intended that the armature, after having struck the gong, shall be replaced in position for another blow by the magnet itself, but by the attendant or automatically, either directly or through some well-known or suitable mechanical or electrical contrivance.

The direction in which the coil of the polarized relay R is wound is such that a current coming from the battery X will cause the armature a to be attracted toward the contactstop a.

The wire forming the coils of the polarized relays 1t and R is likewise wound in such direction as to cause their armatures to be attracted toward contact-stops a M, &c., when a current from battery X passes, while a current from the other battery, Y, at G 011'. will cause the armatures to be attracted toward the contact-stops m m &c. The current from battery Y (except when used as part of battery X, as hereinafter described, for other purposes) never passes through the coils of relay 1%, but through armature to directly to line.

It will be easy now to understand what will take place when the station A B or any other desires to call, Let us suppose first station, A, to call. The key K is depressed once and raised immediately,as in the making ofa dot in the Morse system of telegraphy. This puts the screw-stop m in connection with the groundplate G at the same station and closes the circuit of battery X through the electro-magnet H and ground G. This causes a stroke on the gong g by the immediate release of the armature of the electro-magnet H. At the same time the current passes through the polarized relayR and moves its armature, which, in passing to the other side,n, breaks, after a brief instant, its spring-contact with m to make another against a. At station A, where the key has been depressed, the armature a of polarized relay 1t moves to the other side, severing, after abriefinsta-nt, its spring-contact at m to make one at a with the ground-wire. The armature of polarized relay 1%, however, in making contact against stop it, connects the negative pole of the battery Y with the line wire L,'and as soon as the armature a, by pressin g against screw-stop n, (which will take place almost simultaneously with the contact of arrnature a against a, the two polarized relays being constructed alike, except as to their electrical connections,) a complete circuit exists for the current of battery Y from ground G at central office, 0.0111, to ground G at station St. A. Let us examine what this current of batteryY will cause. At the central otfice, C. Ofl'.,it will pass through the electro-magnet M of the dial-indicator and attract its armature, thus putting the welLknown form of escapement in operation. The eseapement-wheel will turn under the action of a spring by halt a tooth in the direction of the arrow, and the hand or pointer fixed to the toothed wheel will leave its stop 3 to point to the figure l on the dial. The current will produce no effect on thepolarized relayR, because it does not pass through its coils, but through its armature to directly to the line L and t0 the coils of the polarized relay It. In this relay it will cause a magnetism the reverse of that just previously received from battery X, thereby causing the armature a. to pass to the other side-viz., from the ground-stop n to the line m; but in thus passing from onecontact to the opposite one there is a lapse of time during which the armature touches neither, and a break in the circuit is the necessary result.

By observing well-known proportions and adjusting the parts of the several apparatus so as to have the relays rather sluggish, as already described, and on the other hand using every well-known method to render the escapement in the dial indicator quick working, (which rapidity the drawing in Fig. 1 is not particularly intended to represent, aiming chiefly to convey an exact idea of the working, 8tc.,) the duration of the break at the end of the armature a is made sufficient to allow the armature of relay M at central oflice, O. Otil, to be drawn by its retractile spring against its back-stop, causing the end ofanother tooth to escape, so that the wheel turns by another half-tooth, and the hand or pointer points now toward letter A of the dial. After the armature a has made contact with screwstop m at station A the line will be open, as the key K, the depression of which closed the circuit, is supposed to have been raised immediately after depression. The electro-magnet M, at central o'i'lice will therefore remain inactive, and the hand or pointer will continue to point toward A. This will indicate to the attendant at central oflice that the callcomes from station A, which is the purpose of the whole arrangement shown in Fig. 1. The attendant will then, with his tinger or by means of any well-known mechanical or electrical contrivance, turn back the hand or pointer against the stop 3, replace similarly the armature a of polarized relay 1t against its screw-stop m and the armature of electro-magnet H against its cores, so that the whole combination will be ready to receive the IIO turn of said armature can be made known to the caller either by the click itself of the armature, or by sight, or by a visible appendage placed at the end of it, as shown by the arrowpoint in Figs. 6 and 7 of Sheet 1, which represent a suitable manner of making the district-boxes to include the instruments necessary at each station, and which will be readily understood by the drawings themselves without any further description. In these boxes the cores of the relays are placed horizontally and the armature is counterbalanced.

The system is practically non-interfering.

' Any station on the line beyond the callingstation being cut off by the armature of said calling-station breaking the line, as explained before, cannot of course interfere, and the calling process is so rapid, on the other hand, that there is little probability of another station calling just at the same time. Still this may happen, and the would-be interfering station might be situated between the original ealling'station and the central office. Two cases, therefore, may present themselves, and I propose to show that in either the call of said would-be interfering station cannot, by any momentary depression of an ordinary key or any depression of the special key, Fig. 5, interfere with the previous call of the original station calling first.

At the would-be interfering station the armature of the polarized relay will either still be on the stop connected with the ground before the current from the battery Y over the line has had time to reach said polarized relay or said armature will have regained already its position against the line-stop. In the first case it is easy to see that the momentary grounding of a section of the line which is yet cut off from communication with the central office can have no effect whatever if the current of battery Y has not yet reached the section of the line permanently connected with the coils of the polarized relay of the wouldbe interfering station, and if said current has reached said section of the line it will notprevent the armature of said relay from gaining its line-contact stop m m 850. At most there can be then a slight delay in the step-by-step motion of the dial-pointer, which continues to go on as soon as'the would-be interfering key has broken its ground-connection. In the second case the momentary grounding of the line by the would-be interfering station taking place after the armature of said station has resumed its normal position and before the armature of the original calling station has done the same can, at most, also slightly delay the step-by-step motion of the dial-pointer, which continues as soon as the ground is removed by the raising of the key at said wouldbe interfering station, and an expert attendant may even detect by a momentary stop on the dial the station from which the interference proceeds.

I have previously stated that when a call was made at any station the key there had to he simply momentarily depressed and allowed to resume its normal position; but to provide against any difficulty which might arise from keeping any key down too long I employ the key represented in Fig. 5. This key is composed of two separate levers, one straight and the other forked. It is inclosed for protection in a box, (for convenience not shown,) from which the rubber knob protrudes. In the drawings the screw-stop m is permanently connected with the axis of the forked lever and also with a spring which presses permanently on a metallic sector, which latter has for its center the axis or pivot of the additional forked lever, so that said spring will maintain said forked lever in any position it may assume in turning around its axis within limits sufficient for the purpose. a is connected with the straight lever. This additional forked lever is metallic. The upper branch of its fork is supplied with two contact-points, 2 and 3. One of them, 3-the nearest to the axis-is terminated by a small insulating-bushing, and does not project so far as the point placed at the extremity of the same upper branch, The lower branch of the fork has a point,. 1, also terminated with a small non-conducting bushing. Said point is placed opposite the contact point 2. There is a sufficient distance between these two points 1 and 2 to allow some play to the back part of the straight keylever. Said lever is metallic and permanently connected with the ground through a. In the drawings it is represented at rest under the pressure of a spring, as in a Morse key. This makes its back part (to the left on the drawings) press upon the non-conducting extremity of the point at the end of the lower branch of the fork, and to force said lower branch of the fork to press down on an outside limiter, 4, below, which limits the play of the fork in the downward direction. In such position no current can pass from m to at through the key. Let, now, the rubber knob be depressed, the left part of the lever will pass from the non-conducting point below to the metallic point above. (Meanwhile the fork will remain stationary, as it has no-reason to move, its center of gravity being by construction on or very near its axis of suspension and the spring to the left pressing upon the sector.) The result will be that a contact will be instantly established, and that a current can pass from m to a. As the rubber knob is further depressed by the operator the left part of the straight lever will raise the fork of the lever by pushing against the metallic point 2. Meanwhile the communicationbetween m and n continues uninterrupted. (I will remark here that itis a rubbing or friction contact.) As this motion of the knob is continued a time comes when the extremity of the left part of the straight lever reaches the insulating-point 3 on the upper branch of the fork. The effect next call. An automatic mechanism which can be readily arranged could restore to their normal positions the pointer of the indicator and the armatures of the relay R and of the electromagnet H in their original positions. There are some old and well-known printing-telegraphs which have such a mechanism to carry them back to unison after each letter has been printed. Supposing, now, that at station 13 the key K is depressed and raised immediately, let us examine how the call will be received andindicated at the central ollice, 0. Off. The momentary depression of K momentarily connects m with the ground-plate G and this completes the circuit, which includes battery X, relays R R R and ground-wire at station B. The circuit thus completed does not include the ground-wire n to G at station A. The positive current from X thus set up, as explained before, operates the alarm H g d and moves all the armatures a a a to the righthand stops it a n It is able to do this because, by reason of the sluggishness with which the spring-contacts are broken, the current has time to make itself felt to the end of the line before the contacts at m m, 820., are broken by the motion of their respective armatures. The instant this is done a new circuit is established, which passes from the negative pole of battery Y, through M n a L R a n, to earth at G. This current, acting on the magnet M, releases the escapement of the indicator at 0. Off, as before, and the pointer advances to 1. Having done this, the relay It, more sluggish than the indicator apparatus, becomes aifected and draws the armature a to the left-hand stop in. The break caused by the passage of a from n to m opens the circuit, releases the armature of M, and the pointer advances from 1 to A, as before. As soon as a touches on the circuit of battery Y is again completed, but this time through M a a L t a m L R a n to ground at G The current thus set up again moves the pointer at central oflice another notch-vim, from A to 2-and throws the armature a? from n to m and the break caused by the passage of this arm ature again permits the pointer to move another notch-fro1n2 to B. \Vhen this isdone the pointer rests there, and as the line is then open at the calling-station B and not closed anywhere beyond, no more change takes place, and the attendant at central office perceives that it is B that has called.

Should there be more stations beyond B, the process of calling from such fart-her station would be the same, one complete to-andfro motion of the armature of the indicator at central ofliee being caused by the automatic consecutive movement of every polarized relay in the line between thecalling-station and the central otfice, including the relay at the calling-station.

To recapitulate the operation: Each time the circuit of battery Y is completed the armature of M in the indicator is pulled by its magnet, and each time it is broken by the passage of an armature from n to m n to in, &c., the armature of M is drawn back by its spring. Each make of this circuit at a n, &c., and each break in passing from n to m, n to m, 820., causes, therefore, a motion of the armature of M, which can be made visible or be registered at central oliice. The circuit is normally open, but is complete, except that there is no distant ground-connection. Depressing a key at any station grounds the line at that station and completes the circuit from the central office to the station where the key is depressed. The armatures bein gin the normal position of rest that is, all to the left, on m m, &O.illl6 circuit thus completed includes the battery X, the positive pole of which goes to line. The effect of this is to first ring the very sensitive alarm H. g d, and then immediately to simultaneously throw all the armatures and break their contacts at m m, &c., and pull them toward at n W, 810. As soon as the armatures have moved away from m m m the battery X is cut out by the motion of the armature a, and as soon as they reach at n n the contact ofa and n at central ofliee puts the negative pole of battery Y to line, and this moves the pointer one notch or half-space from a letter to a number. As this current does not pass through the coils of relay B, it does not move armature a. It does pass, however, through the coils of R and moves the armature a toward m, but it does not at this instant affect any station beyond A, because the line is grounded at G and open beyond A. The movement thus caused in the armature a from n opens for an instant the circuit and allows the spring of M to move its armature and the pointer connected with it another half -step on the dial. The moment a touches on a circuit which includes battery Y is again completed through station A to n at B, and thence to ground G and this new completion of a circuit which includes battery Y moves the pointer another half-step to 2. This current has no eli'ect on armature a, as already stated. It has no effect to move armature a, be cause that is already against m, but it serves to pull armature a from n to m and the break thus caused permits the retractile spring of M to again move its armature, which allows the pointer to move another half-step from 2 to B. If the person at B has previously taken his finger off his key K as he should have done, the circuit will remain open and no further change will take place in the pointer at central oilice; butif he keeps the key depressed too long the current so continued will move the pointer to 3, and when he takes it off will move it to O. This inconvenience will be remedied by a peculiar key which I have devised for the purpose, and which is shown in Fig. 5. It should be remarked that the callingstation receives notice by the return of its armature a, &c., to its original position through the operation of battery Y that its call has been received by the central oflice. The retion.

of further depression will be to sever the contact of the left branch of the strai'gl'it lever with the metallic point 2, and the communication between in and a will be thereby broken. The pressure continuing on the rubber knob, the insulating-pointl will be brought to bear below the left part of the straight lever and stop its further progress inits upward course.

It is obvious that the continued depression of the rubber knob to the right will cause no inconvenience, as the communication between m and n is henceforth severed, and thus the depression of this key, no matter how long continued, will only make one momentary connec- For greater safety a strong limiter is placed below the knob, (or in some other convenient position,) and one push 011 the knob, no matter how violent, causes the key to perform all the operations I have here described without injury. \Vhen the pressure is removed from the rubber knob the left part of the straight lever pushes downward the lower branch of the fork until it stops against the outside limiting-screw, 4t, and the apparatus is restored to its original position.

It is obvious that the insulating material might be inserted in the straight lever instead of in the fork.

In Figs. 10 and 11 Ihave shown some of the forms of the same key which may be cheaper or stronger. The proportions should be such that the duration of the contact will be at least long enough to work the relay.

The total amount of battery-cells used in Fig. 1 at the central office, G. Offl, can be reduced one-half by adopting the plan shown in Fig. 9, in which the battery Z is reversed by the movement of the armature of the polarized relay 1t, and fulfills in turn the function of battery X and that of battery Y of Fig. 1. The disposition shown in Fig. 1, however, though requiring more cells of battery, offers a greater simplicity of contacts at the armature of the polarized relay R.

The resistance r r at the different stations can be dispensed with by adding to the dialindicator the apparatus shown in Fig.8, which I will now describe.

Below the flat ring of the dial, where the numbers and letters 1 A 2 B 3 O are marked in Fig. 1, there is at a little distance another ring of metal cut in sections, (one for each letter,) as represented in Fi 8, and having a certain thicknesssay one-eighth of an inch the different sections being held in the position shown by some insulatingsupport. These sections are connected one with the other, as represented, through resistance-coils and electl.() magnets llfll 1/11 fill IN/J ll, SELL The electro-magnetsf f f, 850., are all of the same resistance and of the same inductive power as the magnets of It It B &c., and the resistances r 1" are respectively equal to the resistance of L L L of the line. In practice, however, they could be made all alike, averaging the resistance of each section of the line from one station to the next. The

sections should be so arranged that the break shall come between 1 and A, 2 and 13, &c.

The electro-magnets ff, &c.,.could be dispensed with in practice if simplicity of construction and cheapness are an object. In this case they would have to be replaced by the same amount of resistance. 'Another way to dispense with them without sacrificing altogether their inductive capacity would be to wind the increased resistance-coils r 0', 850., single, instead of double, as usual. The hand or pointer of the dial in Fig. 1 carries at the same level with the lower ring of metallic sections an articulated arm, P, bearing at its end a metallic roller or wheel or rubbing-spring. The articulated arm is pressed by a spring, P so that the wheel will roll with some pressure over the inside circumference of the metallic sections of the lower ring. This apparatus is made part of the line between a and M, the roller being permanently connected with, point a and the farther section with M, as indicated in drawings.

The operation of the improvement is as follows: In its normal position shownin the draw ing a current passingfrom n to M has to traverse all the resistances and magnet-coils W 0* f, &c.; but, as the hand carrying the roller moves in the direction of the arrow the total resistance between a and M decreases step by step as each section is rearched. For instance, when the hand indicates station A the first bobbin of resistance, r and the first magnetic eoil,f*, will be subtracted from the total resistance between a and M, and it will be noticed that meanwhile the resistance of the section L of the line and ot' the relay R will have been introduced in the circuit. The other coils and resistances are successively cut out as the number of the stations calling or to be called increases.

The purpose of the improvement is to render uniform at all times the total electrical resistance of the circuit as well as its magnetic retardations, to insure uniformity of adjustment not only at the dial electro-magnet M, but at all the stations. This object can also be attained by placing a proper resistance in the grountlwire at each station, as shown in Fig. 1 at 1' N, &c., as already stated. This would, of course, simplify the construction of the dialindicator at the central office; but the total amount of resistance to be used would be far greater, as the first resistance-coil at station A would have to be equal to the resistance of the rest of the line, instruments included, be yond screw-stop in. The resistance-coils at the station would have also to be frequently altered whenever more stat-ions were inserted or added to the line, while the plan shown in Fig. 8 is free from such an objection.

I will now indicate a modification of the apparatus shown in Fig. l, by which the central office can put itself in direct communication with and can call and talk with or telegraph to any station on the line.

The arma-tures a a a &c., being in the positions represented in the drawings, and the far end of the line being permanently grounded and the positive pole of battery X disconnected from the line, (in which case the system cannot serve for calling the central oflice from other stations,) the attendant at the central offiee has but to connect it again by a key or other suitable contrivance at central office to cause immediately all the polarized armatures a a a at all the stations, central oflice included, to go against their respective ground screw-stops a a of, 8:0. Then the same opera tion takes place as described beforeviz., the battery Y, being put to line, will bring back in succession all the armatures except that of the central offiee, from the first to the last one, against their stops m m &c., thus causing, as explained before, by the successive make and break, the dial hand or pointer to indicate all the stations, from the first to the last. I will, however, observe that in this case the dial-pointer will move by half a tooth more than in the former case and indicate the figure marked on the dial just after the letter intended to represent the last station, and this because the line in the present case is grounded instead of being open, which causes the armature of dial electro magnet M to be attracted once more after the break caused by the passage of the armature from one contact to the other at the last station.

Nowletus'suppose thatduring this successive operation of bringing back by current of battery Ythe armatnres to their original position there is at central oflice a contrivance to enable the attendant there to break thecircuit of battery Y and to connect the line-wire to ground at central oflice after its current has had sulficient time to restore to their original position the armatures of the relays at all the stations as far as, but exclusive of, the station to be called, and before said current has had sulficient time to affect the relay at said station to be called. It is plain that the armature of the latter station will remain against its ground contact, and there will be then a direct circuit from the ground at central office to ground at the station to be called through the polarized relays at the stations situated between the central office and that station. By having, for instance, a sufficiently-seiiisitive polarized sin gle-stroke bell inserted in the ground-wire at the station to be called, (and all the other stations are to be fitted up like the one which we now consider,) and by using for this bell a battery which is considerably weaker than X or Y and of the same polarity as X, and not strong enough (with the resistance of the line and relays and artificial resistances at each station, or as shown in Fig. 8) to move the armature of any of the polarized relays, the attendant at the central office can ring said bell and call said station, after which process said weak battery can be disconnected and the ground restored at central oflice. A telephone, for instance, can then be inserted or switched into the ground-wire both at the central otfice and at the called station. Direct communication is thus established. Instead of the bell, a telephone can be kept in the ground-wire and be used for calling by means of a circuit-breaker or buzzer at central office. This, however, may expose the telephone to injury.

It is plain that the conversation between the central oifice and the station called cannot be interfered with, for the relays and their arm atures at each station are placed in a closed box, and, as there is no current on the line, said armatures will keep the position they have.

The telephones at all the stations are placed on ground-wires, and said ground-wires, not being in contact with any armature except at the two communicating stations, cannot be used to overhear what is said between the stations. As for the stations beyond that which has been called, the linewire which otherwisejoins them to said station is open at the end of the armature of the polarized relay there, and they are thus cut off from any communication with the part of the line be tween the central otfice and the station with which it wishes to communicate.

I will now describe the additional features introduced in order to call any station from the central office, and which are shown in Fig. 10. The wire which is permanently attached between the battery X and the battery Y is permanently connected at its other end with the back contact-stop of a double-pointed Morse key, Q, the lever of which is permanently connected with the ground, while its front contact-stop is permanently connected with the negative pole of battery Y. The key Q carries below its front part (the part which supports the rubber finger-knob at its end) a soft-iron armature, opposite which is .placed an electro-magnet, M. One end of the wire surrounding its cores is connected with the axis of the dial-pointer, while the other end is connected with the metallic rim or circumference of the dial through a local battery, L B. Said local battery could be, for economys sake, a part of battery X tapped for this purpose.

Around the dial, and opposite each letter or mark representing the respective stations, I place, as is well known in some forms of transmitters for dial and printingtelegraphs-forexample, Siemens dial-tclegraph-tinger-knobs, each fixed at the extremity of a brass rod or pin passing through a hole bored in the metallic circumference or rim of the dial. Each brass rod or pin is traversed near its extremity crosswise by a smaller brass pin, or is there provided with a collar, which prevents it from getting out of the hole by the action of the retractile spring, which is placed around said rod outside the rim of the dial, between said rim and the finger-knob. The axis which carries the pointer P of the dial also carries an IIO arm, 0, which moves in the plane of the pins Q Q and Q, and is about one station in advance of the'pointer P, as shown. The axis and this arm are insulated from said metallic rim of the dial. This arm 0 has affixed near its free extremity, on the side toward which it moves when revolving, a V-shaped metallic spring intended to furnish a friction-contact when in its revolution it meets with one of the depressed fingers, rods, or pins projecting in side. Thelcn gth ofthe pointer, however, is such that its solid partwill itself meet with said finger rod or pin, so that it will be impossible for said pointer to go beyond the point where it is intended that it shall stop, while at the same time the contact there will be firmer.

-One wire of electro-magnet M at central office, G. ()ftl, Fig. 10, leads to contact-point a, as before. The other wire leads to the lever of a key, K the back contact-stop of which is connected with the negative pole of battery Y, while its front contact-stop is connected with battery Yat or about the middle, or rather at such point between its cells that the number to the right in the drawings shall be less than the number of its cells at the left, as circumstances may require. This latter precaution is taken for the following reason: The right part of battery Y, being used when key K is depressed to work the polarized callbell of any station, must send to the line a current considerably weaker than the current of battery X, so that the armatures of the polarized relays will not be moved by it. The call-bells are indicated by 1) N, &c.

The operation of the above-described feature is as follows: The armatures a a, 850., being on their line'contacts and the circuit closed through them, but having sufficient resistance to prevent the relays 1% B, 850., from being affected by the current from battery X alone, the depression of key Q adds the current of battery Y to that of battery X by transferring the ground from between them to the negative pole of battery Y, and the increased current throws the armatures of all the relays on the line against their respective groundcontact stops at n, &c., where they stay. Thisaction will be utilized, as hereinafter explained, in establishing an intercommunication, which will enable at the same time several stations on the line to communicate each with his neighbor on either side.

If, now, before key Q is raised one of the fin ger-knobs around the dialfor example, that corresponding to the letter B, representing station B-is depressed and kept depressed either by the finger or by any piece of mechanism or locking device adapted to retain it depressed, (as by a slot and pin operated by giving it a quarter-tram) and key Q is then raised, the batteryY is put to line through M, and the process of raising in succession the armatures along the line, as described before, goes on until, by the work of the dial-escapement, the arm 0 makes contact against the end of the pin or red affixed to the depressed finger-knob, that of Q in our example. This closes the circuit of the local battery L B through electromagnet M, which attracts its armature, thereby causing a new depression ofkey Q. This in turn breaks the ground, and thus cuts off all battery from the main line. A through-circuit is thereby established between the central office and station B, and grounded at B through its ground-contact n ready to signal or talk with B. The attendant at the central office can, by a repeated stroke on the knob of the key K work the polarized bell of station B, as each such stroke introduces in 'the circuit the part of battery Y to the right in the drawings. A telephone or other instrument can then be inserted in the line by an automatic or some other wellknown switch. Observe that the polarity of the current which rings the bell is the same as that of the current of battery X when the latter current passes over the line. This is for the following reason: The positive current of battery X can never pass over the ground-wire a G a G 850., at any station, as it is always automatically cut off by the break caused by the motion it gives to the armatures before they reach the ground-stop a, 8tc. The negative current of battery Y, however, passes repeatedly over said ground-wires at the stations. The polarized bell is therefore so connected that said negative current of battery Y cannot affect it. Therefore the key K has been so combined and arranged as to send over the line a current of the positive polarity required to work said polarized bell, but still sufficiently weak not to move the armatures of the relays between the central office and the called station against their ground contact stops. After calling, the assistant at the central office takes hold of his telephone T, which might be ordinarily kept short-eircuited by some well-known switch to save it from being spoiled. The person at the station called also takes hold of his telephone, which can be similarly protected when not in use, except in the case where the telephone itself is to be used instead of the signal-motion of the bell, as in some systems. WVhen the connectionshave thus been made conversation can'go on between the central office and the called station. When it is ended both replace their telephones, and the assistant at the central office replaces the apparatus in its original position by pulling out the pin Q" and putting the pointer back to zero and then afterward moving the armature a, to the stop on.

In the system first described, by which a station calls the central oihce, the line is open at its extremity. In the systems next described, by which the central office calls and communicates with the desired station, the line is grounded at its extremity. I will now combine both into a system uniting the results and advantages of both and some more besides. For

this purpose I ground the extremity of the line beyond the line-stop m of the most distant station through a resistance, R, sufficiently high to so weaken the current of battery X that when it has no other ground-connection the battery X, which is normally kept on, will not move the armatures away from the linestops m m, 850., but at the same time sufficiently low, that the addition of another battery to battery X by an appropriate key will be able to cause the armatures a a (o 850., of all the polarized relays to pass to the opposite ground-contacts n a W, 8150., contact a becoming connected with the ground by means of the same key. I thus have a line which at the pleasure of the central office is open or closed at its extremity.

Instead of that resistance E I may use any of the devices well known to electricians which leave the line practically open for some currents and practically closed for some others.

I will now describe an improved method of combining the two systems. At the extreme station (see Fig. 10) 1 make the polarized relay much more sensitive to a weak current than any of the other relays. The resistance R (which, as before stated, must be so large that when it is in circuit the batteryX will not work any of the relays) is between the left-hand or line stop of said relay and the ground G while between the ground-stop and the ground-plate Gr (supposing B to be the last station) the artificial resistance corresponding to r 1, Fig. 1, is M1, or, as in the drawings, is omitted. By means of the key Q at the central office I add to batteryX the cells of battery Y, (which battery, for the purpose, need be no larger than is required for its ordinary work in the system first described,) and I thereby obtain 011 the line a current which, by reason of the large resistance R will not be strong enough to work the relays at the intermediate stations nor at the central office, but will be strong enough to work the more sensitive relay at the last station. This will throw the armature at that station to its right-hand or local ground-stop, (corresponding to n,) and thus first break the line which passes through the high resistance R and make a more direct ground. The circuit thus instantly comes into the condition of the system previously described, and the current is immediately strong enough to throw all the armatures of all the relays, including that at central office, to their stops at n, &c., just as battery X did in the system pre 'iously described. This movement of armature a, to contact n throws on battery Y, by means of which the operator at central office can call the desired station, as already described. On the other hand,as batteryX is all that is normally on the line, and as it, by reason of the resistance R, has no effect to move the relays any more than if the line were open at its extremity, any station can call the central office by depressing its key and grounding the line at its own station, as already described with reference to Fig. 1.

Finally, by the addition of a few simple attachments to the apparatus already described, I am enabled to obtain what I will term direct intercom m unication between the stations. For this purpose I adapt to the armature of each of the polarized relays a metallic plate or band, t t &c., insulated from the armaturelever proper, though mechanically forming body with it. The end of said metallic band nearest to the pivot of said armature is connected with a spring cut-out provided with a hook, from which hangs a telephone,T", at station A, and T at station B, and so on at other stations. The other ends of said metallic bands, when necessary, as explained afterward, come in contact with suitable stops (1 at station A, g at station B, &c. The screwstop q is permanently connected to the line screw-stop m at station A, and g to m at station B, and so on at the other stations.

I will show first how the central oflice can put all the stations in communication each with the next on either side. All that is necessary to do at the central otlice for this purpose is to simply add for an instant the current of battery Y to that of battery X by key Q, which throws all the armatures to their ground-stops n n M, &c., and likewise makes contact between the metallic bands t t, &c., and the stops q g &c. Thus telephone T* at A is in circuit with T at B by the following circuit: G, T, plate t q m L, coils of R armature a and its terminal spring-stop n bell D (which may be short-circuited, if desired,) T and ground G In like manner telephone T is in circuit with the telephone in the ground-wire of the next station beyond, if such there be, and so on, each station having one telephone in circuit with a telephone at the next station to its right and another telephone in circuit with a telephone at the next station to the left.

I shall hereinafter show how one telephone can, by an appropriate switch arrangement, be made to sut'tice for each station, instead of two.

The above method can be practically used and with great advantage and economy of time when several stations on the line at the same time want to communicate with the adjoining station on either or both sides.

I will here also remark that whenever the central office puts itself in communication with any stationl3, for instanceall the stations beyond are put in communication each with the adjoining one on both sides. In this case the station A would alone be entirely out out. This arises from the fact that the armatures of the polarized relays at all the stations, from B inclusive to the end of the line, are making contacts at (1 850., and at M, &c., which furnishes each station with a direct circuit with the adjoining one on each side, as explained before.

I will now describe how the central oflice can put any two stations in intercommunication without fear of interference after the circuit has been established. For this purpose I insert in the section of the line L, Fig. 10, a condenser, J, of sufficient capacity for the particular purpose to be described. I keep this condenser ordinarily out out or short-circuited by a switch, J. Between the alarm magnet H and battery X, I place a switch,s 10. When the handle of said switch is to the right, beyond the first.contact-button, the battery X is disconnected. When said handle is on first button a part or section of battery X is connected. Another fraction or section of X is added when the switch-handle is on second button; and, finally, all the battery is on when the handle is on third button. There could be more buttons than represented. This device serves to put the whole battery gradually onto the line when so required.

Suppose, for instance, that it is required to have station B in private communication with a station (not shown) called D, station 0 bein g intermediate. The central office putsitself incommunication,bythemethodpreviously explained, with station D, calls it, and warns it to keep listening with its telephone, as station B wants to talk to it. This done, central office restores its apparatus and all the armatures at and beyond I) to their position of restthat is, against their line-contacts. The restoration of line through D and beyondis not, however, essential, as the current for moving the armatures to their ground-contacts at stations AB 0 could be allowed to pass to earth at station D. Then the central office puts itself in communication with B, calls it, warns it that D is actually listening, and orders it to take hold of its telephone T, and after it has heard the click of its armature, or rather after a few seconds, to depress at least once its key K 5 lows: Having only the armatures ofthe stations Band 0 to raise to obtain the desired result, he depresses first dial-finger key corresponding to station D, then lets go dial-finger Q to its usual position of rest. This breaks at the end of the arm the circuit of electro-magnet M. The armature and key Q recede, the ground is reestablished betweenXand G, batteryYis to line again, and throws armatures ot'B and 0 against their line-contacts m &c. Then, the key Q, being again depressed by the attraction of M on account of the circuit ofL B being closed by the end of the arm 0 meeting the depressed dial-pin, the battery Y is again out off, and the direct ground for the main line restored at the central office through a n M K Q G. The attendant at the central office switches off battery X by means of s 20, disconnecting the whole of it from magnet H. He replaces armature a against contact at, opens condenser 6 5 cut-0H switch J replaces dial-pointer to zero,

(the order in which the two preceding operations are performed is immaterial,) and finally he switches in gradually battery X by means of s w. This could be done in some other wellknown mannerfor instance, by using alarge resistance between battery X and magnet H, or near the condenser, and decreasing it graduall y by an appropriate switch. This puts battery X gradually to line through condenser J without causing any current to the line, which current would be produced were said battery X suddenly wholly connected to condenser J. The line is now open at J, so that no constant current from battery X can pass; but as soon as station E, as previouslyordered, depresses its key K a sudden impulse from battery X (which the condenser J is large enough to transmit) goes through the line as far as ground G at station B. This impulse throws armatures a a c against their contactstops it n a", when battery Y is suddenly put to line through condenser J and restores immediately, by an impulse through said condenser, the armature a against the line-contact stop m, and the pointer of the dial moves as usual. The attendant must, as soon as he puts the battery X to line by switch 8 to, depress finger-key Q3 on the dial, because a little before the armature a touches m the battery Y must be cut off by key Q, and the contact of the arm 0 with Q eii'ects this. The desired result is now obtained. Station B is in communication with station 1), while the central office is itself in connnunication with station B.

It will be observed in the foregoing description that the armature a of the alarm H Fig. 10, is caused to move to the stop a by its retractile spring when the magnetism of H is destroyed or weakened by battery X at the same time that armature a moves to n, and that the armature a may be returned to p at the same time that to is returned tom. I can therefore dispense with the relay It by connecting the line-wire L with to instead of a, the wire from battery X with m", with which a spring is connected so as to bear against the spring prolongations of the armatures of the relays at the several stations.

There would be a certain advantage in using a metallic circuit with this system, because the extremity of the line will be at the central office, thereby dispensing with the contrivances which I have described for giving a direct ground instead of through the resistance R as already described.

It will be observed that as the call is given from any station by grounding the line there, any accidental ground on any part of the line will announce itself and indicate its location on the dial.

To avoid the expense of two telephones at each station I employ the arrangement shown in Fig 13. A wedge, W, made of rubber, with its sides covered with metal, as shown, is mounted so that it can move between two spring-jacks, W" W The weight of the telephone, which is hung on a hook attached to the lever, normally keeps the wedge in contact with the lowest side, and in this position the connection is suitable to talk to the main ofliee or to any station between the one in question and the central office. To talk to a station beyond, the wedge must be pushed to the upper springjack. The letters of this figure show, by comparison with station A of Fig. 10, how the apparatus is to be connected with the rest at the station.

No particular description of the devices shown in Figs. 2, 3, and 4 is needed further than to say that the points '0 and 10 indicate the escapement-teeth of the dial-indicator, and that no and i are devices for adjusting the armatures of the relays shown. These devices are to replace the magnet M.

In using the apparatus represented in Fig. 10, the condenser, after it has been discharged by the grounding of the line at station B in the example given, remains in circuit when a current from the battery Y is sent over the line by the contact of armature a with the stop or point a. In order that it may be cut out automatically, the condenser J, with its switch J, is placed between the coils of relay B and the stop m, as shown in Fig. 14. This figure also shows connections for employing both batteries X and Y for changing the condenser. In putting the battery to line through the condenser the key Q, must be kept depressed so that the pole of battery Y will be connected with the ground, and X and Y will constitute one large battery. After the armature a has moved to its contact n the key Q must be released, so that the negative pole of battery Y may be placed to line.

When the Hughes apparatus is made to take the place of relay R, as shown in Fig. 12, the condenser and switch are placed between the coils of H and m". I

Instead of employing the condenser at the central office, a small condenser may be employed at each of the stations, the position occupied by them, which is the same for all stations, being indicated in Fig. 15.

The operation of these condensers in the example given is as follows: The armature of the relay at station D being on the ground-contact, no current passes from X on account of the condenser. When the key at station D is depressed a direct momentary ground is made at B, so that the current from X throws the armature at stations A and B and 0 off to their right-hand contacts, and then the batteryY acts as usual until out off by the closing of the circuit of station B by means of the pin Q". The condenser at station A in the example being charged, the relay 1t is affected as it it had a direct ground. The switch 8 w is employed as before described.

The key shown in Fig. 16, which is otherwise constructed like that shown in Fig. 11, has the end of the lower branch of the fork wholly made of metal, while the back part (to the left in the drawings) of the straight lever of the key bears under its lower face a sheet or band of metal, 70, insulated from the rest of the lever by an insulating substance, such as hard rubber. (Represented by a black line in the drawings.)

Fig. 17 shows how a contact harder than rubber, ivory, or other insulator can be obtained by boring a hole through the metallic body of the upper branch of the fork and forcing or screwing in it a hollow insulating-bushing, which in turn will receive a pin or screw k, of hard metal, against the head of which the left upper extremity of the straight lever may rub. Hard contacts could also be obtained in many ways substantially the sameviz., by covering the soft insulating substance with a harderone not connected with the body of the key. A hard contact may in like manner be obtained in the key shown in Fig. ll.

When the key shown in Figs. 16 and 17 is employed the line-wire L supposing the key to be located at station B, instead of connecting directly with the stop an, is carried to the insulated plate of the key, (preferably near the pivot,) and thence is in electric connection with m through the key-levers, which are kept by the spring of the key normally in the positions shown. When this key is depressed its motion not only grounds the line comingfrom the central oflice through the relay-armature a and contact-stop m, but also just previously breaks at the key the main line, which norl mally extends beyond the, station. The advantage of cutting off the rest of the line before giving a new ground is well known; but its main purpose in this invention is to help to put in communication from the central office any two stations, such as B and I).

In the method already described of obtaining said result when all the operations had been performed as far as the moment where it remained only for station B to depress its key K to put itself finally in communication with both central office and station D, the line from central office was partially grounded at station D through its bell and telephone, the impulse to be caused on the condenser, inductiolrcoil, or other well-known or suitable electric appliance at the central ofiice was only due to the portion of the line grounded beyond station B, being momentarily short-circuited by key K at station B. In some cases this impulse might be insuflicient, and render it necessary to have at the central otfice avery delicate instrument to make it sensible. Now,

IIS

byjthe use of this key, Fig. 16 or 17, said impulse is considerably increased as the partial grounding of the line at station D is cut off, as explained, by the first operation of said key; then the ground-connection is afterward made by further motion of said key, and an electric impulse is fully produced on the condenser, induction-coil, or other suitable appliance at the central office.

Instead of using the condenser before described, the arrangement at the central office represented in Fig. 18 may be employed for obtaining intercommunication between any two stations, it being used in connection with the key, Figs. 16 and 17, (which, when depressed, breaks first the section of the line beyond, makes a ground, and re-establishes its own connection with the section of line beyond,) at all the stations on the line.

At the central ofiice an ordinary relay, H, of about the same sensitiveness and resistance as any of the polarized bells at the stations, has one end of its coils permanently connected with the ground G. The other end of its coils is connected with its front stop-contact, m h.

A section of the battery X on the side of its positive pole (to the left in the drawings) is detached from said battery. The strength of this section is about the same as that of the batteryY on the side of its negative pole, (to the right in the drawings,) which is used in combination with the calling key K The positive pole of said detached part of battery X is connected, as before described, to electromagnet H, while its negative pole is connected wit-h the pivot of armature a h of relay H. The positive pole of the remaining larger part of battery X is connected to the back contact-point, a 7i, against which said said armature a it normally rests under the force of its retractile spring. This additional feature is used and operates as follows: Let us go back to that point in the description where the central office, wishin g to obtain the in tereominunication between stations B and D, had given warning to station B to hold its telephone for conversing with station D, and to depress its key K an instant after hearing the click of its armature, (in its passage from ground to line contact.) These directions given, the attendant at central office puts himself, in the manner already explained, in direct communication with station D, and while he keeps depressed the knob on the dial corresponding to station D he moves, byhand orby well-known or suitable means, the armature ah of relay H from its back contact-point, a h, to its front contact-point, m h, against which he holds it until he has moved in the same manner the armature a of polarized relay R from its contact a to its contact m. By this operation a circuit is made from ground Gr through relay H, its front contact, m h, armatureah, smaller part (to the left in the drawings) of battery X, (the rest of which is cut off at n h,) and thence through electro-magnet H, relay R,

contact m, armature a, and line, as usual, to the ground at station D, after traversing there the bell and the telephone. This current is insufficient to cause the armatures between the central office and the station D to pass from their line to their ground contacts, though it weakens their pressure against 19 850.

It is to be noticed here that a stroke against the bell at said station (with the hammer remaining close to the gong) warns it that the main office has made the circuit ready for the next operation to be performed by station B. I will also remark here that it is not impossible for station B to know also the condition of the line, for the solid part of its armature a will, it properly adjusted, recede at this moment from its contact 19 under the influence of the weak current from the left part of battery X, although the spring at the end of said armature will still preserve its line-contact m The assistant at the central office now lets go the dial knob corresponding to station 1), brings the arm and escapement-wheel to zero, and immediately depresses the dial-knob corresponding to station B.

All the operations can succeed each other rapidly, and can be automatically performed by some appropriate mechanism. The amount of time for their performance can be practically ascertained once for all. It increases with the number of stations situated between the central office and the two stations to be thus mutually connected, and the warning to be given by the central office' to the stations is to be made accordingly. I

It remains now only for station B to depress once its key K which is of the character shown in Figs. 16 and 17. This key breaks the circuit from ground G at central office to ground at station D, and releases the armature a h of relay H at central office. The said armature severs its ground-connection at m h, and by coming, under the action of the retractile spring, in contact with back-stop n h re-establishes the connection of the left part of battery X with the rest, thus restoring the battery X to its full amount.

I will here remark that by the breaking of the circuit as soon as key K is depressed the hammer of the polarized bell of station D, which was close to the gong, moves away from it, thereby warning station D that the key has just been depressed at station B, and that its connection with it can begin almost immediately after such back motion of the bell-hammer has taken place, for when, by the continued depression of its key. K a ground is made at station B, the whole current of battery X will, in the manner formerly described, move the armatures a a (6 from contact-points m m m to their contact-points n a n BatteryY now, in turn, in the manner explained, brings back armature a against its contact m but theprocess stops there, as the depressing of dial-knob Q then brings the local batteryL B into action, so that the key-armature of electro-magnet M cuts off batteryY and grounds the line at central oifice. The latterris in direct communication with station B, the armature of which is now on its ground-contact, while station B is itself in direct and private communication with station D through the armature of station G, which has remained on its line-contact. All the stations beyond D, being on their ground-contact, are in commu-- nication each with the adjoining one on both sides. As there is no battery now in any of the circuits, there is no possible interference. When station 13 has done talking with station D it so advises the central office. The central ofiice can also, while B and D are conversing, call the attention of B by working its polarized bell with its call-key, to warn it, for instance, that its time is up. The central otfice can always, at its own wish, restore the line all through to its original condition by simply raising the dial-knob corresponding to station B in the above example. The current of batteryY restores all the armatures to their primitive positions against their line-eontacts,after which armature a and dial'arm can also be restored to their original positions.

Instead of cutting the battery X into two parts and connecting them and the groundwire with the relay H, as just described, at the central office, I can make use of the following arrangement, represented in Fig. 19: Between electro-magnet H and battery X, I place the relay H and a high resistance, H connected thus: positive pole of battery X with the pivot ot' armature a h, the back contact, n h, of said relay with one end of the coils of eleetro-magnet H, as represented, and with one end of the resistance-coil H the other end of which is connected with one end of the coils of electro-magnetH. Thefront contact, m h, is connected with the other end of the coils of electro-magnet II. It operates as follows: WVhen brought in use the armature a h is moved against its front contact, the current of battery X is forced to traverse the elec' tro-magnet H and the resistance H, the amount of which is such as to weaken said current sufficiently to prevent it from moving any of the armatures of the polarized relays on the line; but as soon as the circuit is broken, as in the former case, the armature a lb of relay H returns against its back contact, at h, first breaking the circuit for a short instant between electro-magnet H and battery X, and then connecting the two latter apparatus by a circuit of practically no resistance through contact a h and armature a it. Another arran ement is shown in Fi .30 where the conelectro-magnet H and resistance H". It is, however, to be feared that by this last plan the armature a It may return to contact m h before reaching back contact, a h, in case the break made by the key of the calling-station be of too short duration, while the plan in Fig. 19 is free from such objection. A modification of the connections is also shown in the connections in Figs. 18 and 19. The contactpoint a of polarized relay R, instead of being directly connected with electro-magnet M, is connected with the lever of call-key K while the back or rest contact of such key is connected with one end of the coils of electromagnet M, the other end of which is connected with the negative pole of battery Y. This modification has the advantage of cutting off the electro-magnet M while calling a station.

The method just described with reference to Figs. 18, 19, and 20 for establishing intercommunication between any two stations can be extended so as to enable any station to call the central otfice and the central office to call any station. To this end the high resistance at the end of the line is dispensed with, and said end of the line is then constantly and directly grounded. The last polarized relay, instead of being more sensitive, resembles the others on the line in every respect, and the key which breaks the line beyond and grounds the line at the calling-station is made use of at all the stations. At the central office everything stands as described before when at rest, except that the armature a It has been placed against the front contact, at h, of relay [1, so as to put to the line only the small fraction of battery X, situated to the left in the drawings. In this condition there is through the whole line but a small current, which is insuflicient to move any of the armatures along the line from their line to their ground contact. When a station depresses its key the circuit is broken. The armature a h of relay H at the central olfice is released and recedes against its back contact, a It, thus putting all the battery X to the line. Meanwhile the depressing of the key of the calling-station, continuing, causes at said station a direct ground, and henceforth the rest of the process of signaling or recording the call goes on as before, with this exception, however, that the dial-h and will indicate, Fig. 1, the number immediately after the letter indicating the calling-station, on account of the end of the line being grounded, thus giving circuit to the current of battery Y, which ca uses the last attraction of the armature ot' dial electro-magnet M.

The process of calling a station from the central oflice with this arrangement is as follows: Things having resumed the position of rest, the assistant at the central oflice has but to first depress on the dial the knob corresponding to the station to be called and then move the armature a, h from its front contact, at h, to its back contact, a h. This puts all battery X to the line from ground G at contral office to the last ground at the end of the line. All the polarized relay-armatures move to their ground-contacts and batteryY comes into play, and the rest of the operation goes on, as previously described for calling from the central office.

Whenever the end of the line has to be extended to one or more stations it saves time, trouble, and expense in the arrangement just described not to be obliged to remove the last extra-sensitive relay and the high resistance used at the last station, as described before, and as represented in Fig. 10. All the stations can hence be constructed alike, the last one as well as the other. The extra-sensitive relay, used formerly at the end of the line, is replaced by the extra-sensitive relay H at the central office, an d in the process last described the central office can always readily regulate the amount of small current flowing to the line, either by regulating the resistance H, if used, or by varying at will the number of cells in the smaller section or left part of the battery X, While formerly, with the high resistance at the end of the line being generally out of immediate and convenient reach, it was more difficult to obtain the same result. It will also, by the last process, become possible to use for the larger part of the battery X the kind of battery used for open circuits, while in the former arrangement, Fig. 10, this was possible only for battery Y. The smaller part of battery X to the left will, however, be preferably a constant-current battery, such as Daniells or its modifications.

A saving in the number of cells necessary at the central office may be obtained by the last-described arrangement, for if there are several lines radiating from the central office the large part of the battery X could serve for several of them, while there could be a sensitive relay, H, with a small battery (corresponding to the small part of the batteryX to the left) for each line. In this case the positive pole of the single large part of battery X would be connected with all the back contact-points of each relay, like H.

WVith the last-described arrangement there is no use of condenser or induction-coil or switch 8 '10 either at the central office or at the way-stations.

I will also here remark that, while a lasting ground occurring on the line in the system shown in Figs. l'and 10 would be signaled and located on the dial at the central office, (which operation can be readily understood, and is an important feature of the system,) said ground would not show on the last-described plan unless it was preceded by a breaking of the circuit, such as can take place when aline breaks and falls to the ground, which is then a noticeable feature of the latter plan. In the former system an accidental break not followed by a ground would not be signaled otherwise than by the well-known use of the galvanometer, and such break would not be ture of the accidental ground is readily known at the central office. If the ground is of long duration, or permanent, the dial-hand will stay on the number following the letter representing the station beyond which the ground has occurred, and as soon as the attendant at the central office replaces the apparatus at the state of rest they reassume their former positions, the dial-hand showing again the same number. On the other hand, if the ground has only been temporary, the apparatus, once replaced in the state of rest at the central office, keeps it, unless there is a periodical ground arising from what is known in telegraphy as a swing, in which case the dialhand will have to be replaced every time it has indicated it. At all events the nature of the ground is known, as aforesaid.

In Fig.2l is shown an apparatus something like a Siemens shuttle, which can advantageously replace relays with the spring prolongation of the armature. The current passes through the shuttle S instead of through the armature. The line and ground contact points are indicated by ma,as heretofore. This arrangement has the advantage of rendering the line and ground contacts steady during the passage of the armature proper from one side of the shuttle to the other, while when a spring is used at the end of the tongue the quality of the contacts varies with the variable pressure of the spring during the movement of said tongue. The small wheel fixed at the end of a spring on the pivoted part of the shuttle serves to maintain said shuttle steady against either one of its limiters. Its position and pressure are adjustable.

In Fig. 22 is represented one manner of varying the contacts and connections so that the shuttle will make the double contacts made by the armature at a station, as in Fig. 10, tor the purpose of intercommunication. Fig. 23 represents another manner of obtaining the double contact just referred to. In these figures the parts in black represent hard rubber or other insulating material. The lettering is made for convenience to correspond with the apparatus at station A. In Fig. 22 the spring or plate t corresponds to the insulated plate attached to the armature in the relay shown in Fig. 10, and is therefore lettered the same. In Fig. 23 the armature itself acts in place of said plate to establish the circuit between m and telephone T*.

It is obvious that various modifications other than those described and within wide limits could be made in my system without departing from the spirit of this invention. For example, instead of having the magnet M connected with the negative pole of battery Y, it could, if a polarized or equivalent magnet were employed, be placed, under some circum- 

